Field of the Invention
Embodiments of the present invention generally relate to a MEMS device and designs for both anchoring the MEMS device and ensuring switching elements switch together.
Description of the Related Art
When making an array of MEMS devices that need to switch together, variations in the processing of the devices result in different threshold voltages for different switches. The processing variations can alter the lateral dimensions due to fluctuations in the lithography of the etch process. Variations in deposition can result in different thicknesses of material and variation in the deposition of the landing regions can result in different roughness values under different switches which results in different amounts of adhesion or stiction. When making a digital variable capacitor, one may want to switch a large area device in order to get a large capacitance change. It is hard to etch out under large areas and it is hard to support large area devices without making them very thick, so it is advantageous to make a large number of small capacitor MEMS switches and switch them together. The problem with this is that the variation discussed earlier results in different switching voltages for the different devices.
Additionally, a MEMS variable capacitor can be built using two plates (i.e., electrodes) of which at least one of them is movable (also called a membrane). As the two electrodes get closer together the capacitance increases. The movable electrode is anchored with a compliant mechanical support. Electrostatic forces can be used to overcome the mechanical stiffness of the support and move the membrane to change the capacitance.
The stiffness of the mechanical support is very sensitive to the mechanical stress, and therefore, the operating electrical conditions for conventional mechanical supports can suffer large variations, widening voltage distributions and reducing reliability. This can be partially corrected by controlling the stresses during fabrication. However, keeping stress under control is not always an easy task.
Therefore, there is a need in the art for a MEMS device addresses the above mentioned stress issues and ensures an array of switches switch together.